The present invention concerns methods and systems for processing seismic data and basin modeling. A correct interpretation of the velocity field within the Earth is necessary to properly image seismic data at its true location and depth in the subsurface. This velocity field can be estimated by a number of methods, the most important and common being the analysis of stacking, or the roughly equivalent Normal Moveout (“NMO”), velocities on Common Midpoint (“CMP”) gathers. A number of other techniques are also used, including the use of multiple constant-velocity stacks of a small interval of the seismic line, signal coherency analysis of the velocity spectrum, horizon-consistent velocity analysis, the application of statics and residual statics corrections, migration velocity analysis and tomographic inversion techniques. In the absence of well data, these techniques rely on information that is contained within the seismic dataset itself for all of the input data, the parameters for determining the velocity field, its consistency and validity. Seismic processing is a robust process that can tolerate errors of up to approximately 10% and still yield a reasonable image. Once well control data is obtained, more realistic values of the true velocity field are available and the new velocities can be used to refine the seismic image. For proper depth imaging of structural anomalies, and for lithologic and stratigraphic identification and detailing, a much lower tolerance for velocity errors is acceptable, generally less than 1%. Structural depths from both well control and seismic data are commonly used as one of the input sources for basin models.
Basin models are simplifications of the earth and its processes with the intent being to track the dynamic evolution of one or more of those processes through time. For example, the processes related to the generation and migration of hydrocarbons is commonly modeled with the intent to determine which of several possible structural culminations may be the most prospective for containing a commercial accumulation. Basin models use data from seismic, well control and knowledge of the geology of the area to construct a numerical model of the region and to track the changes in the various modeled parameters through time to reach a set of predictions that are then calibrated to the known information at the present. The model parameters are then adjusted within geologically reasonable bounds until a successful match and calibration is reached. Prediction can then be made at locations away from the calibration points.
Basin models and seismic processing are traditionally done quite independently of each other by experts that have completely different skill sets and knowledge bases. Nonetheless, there are several areas where the two can be used together for the mutual improvement of each. In the presence of overpressures, seismic velocities are lower than would normally be expected at that depth, amplitudes are suppressed and the presence of multiple pressure compartments and ramps makes the interpretation of velocities from seismic alone difficult. Below salt masses, high velocity high reflectivity interfaces and below rugose surfaces, the Earth filter removes significant amounts of the signal that again makes the analysis of velocities from seismic data alone difficult. Below about 15,000′ (different depths in different basins), the seismic velocities are high and the frequency content of the recorded signal becomes lower, again making the velocity analysis of the data from seismic alone difficult. Basin modeling can provide information on geologically reasonable values for those velocities. A method and process to accomplish this objective is described herein.